1. Technical Field
The present invention relates to inkjet printers, and in particular to an inkjet printer adapted to make a print by propelling droplets of ink out of a print head onto a recording medium being sucked for transfer at an image forming section.
2. Background Arts
Inkjet printers capable of high-speed color printing and costing low have been remarkably widespread. Most types of inkjet printers are connectable to a terminal, such as a personal computer, to take in image data such as letters, illustrations, and marks, produced at the terminal, to print on a sheet. Composite types of inkjet printers have an integrated scanner or facsimile, to take in image data through the scanner and print them, or to receive image data at the facsimile and print them.
Some of those types of inkjet printers include a mechanism to transfer a recording sheet being sucked on a platen plate. The platen plate is arranged in position opposing an array of print heads in the image forming section. The recording sheet is carried by a transfer belt sliding on the platen plate. The recording sheet is locally sucked toward the platen plate by suction forces acting for transfer via the transfer belt. Such a mechanism can prevent recording sheets from getting wrinkles or rippling (cockling) or prevent recording sheets from curling at the image forming section. This allows recording sheets to be free from floating. As a result, it can serve to prevent interferences between a recording sheet and print heads (for instance, print-head eroding interferences), and to retain stable distances (head gaps) between a recording sheet and print heads. This allows for a stable printing and print image quality.
One might have enhanced suction force acting on a recording sheet to attain more stable printing and print image. However, as suction power is increased in places underneath print heads and in their vicinities, entrained air would flow at increased velocities. Such air flows would affect orbits of ink droplets propelled out of the print heads, causing degraded print qualities. Further, as air flows at increased velocities, it would have increased tendencies to induce mist from ink droplets. Such mist would smear recording sheets, causing the inkjet printer to be contaminated inside (machine interior contamination).
The Japanese Patent Application Laid-Open No. 2007-31007 discloses a sheet transfer mechanism for inkjet printers that has airflow controlling means for reducing airflows produced in the sheet transfer direction. This control is made in places underneath inkjet heads and in their vicinities to suppress the formation of ink mist. The sheet transfer mechanism has air conducting holes to be blocked, air conducting holes formed with a decreased density, and air conducting holes formed with reduced diameters, as specific examples of the airflow controlling means implemented at a platen plate. Such airflow controlling means can serve to prevent sheet contamination due to formation of ink mist at a front edge of recording sheet.